1. Field of the Invention
The present invention relates to an optical interrogation system which implements an over-clocking method that increases a read-out speed of a CCD (charge coupled device) detector (in this case part of a spectrometer) which enhances the ability to detect a minute/small biological event on or near a top surface of an optical biosensor.
2. Description of Related Art
Today optical sensor technology is being used in academia and industry to conduct studies associated with detecting a biological event on or near a top surface of an optical biosensor. In such studies, an optical interrogation system is used which has a launch system that couples light into an optical biosensor (e.g., resonant waveguide grating (RWG) biosensor). The light that is resonant with the optical biosensor is then out-coupled (reflected), and is captured by a receive system which analyzes the light to determine whether or not a biological event occurred on top of the RWG biosensor. In particular, the receive system analyzes the light to measure an optical response (resonant wavelength/angle) that indicates whether or not a biological event occurred on the top surface of the RWG biosensor. Unfortunately, such a receive system and in particular its CCD detector, which is used in industry today, may easily be saturated by the received light. Such, CCD detector saturation makes it difficult to detect minute shifts (e.g., sub-picometer wavelength shifts) in the optical response, which means it becomes difficult to detect small biological events on top of the RWG sensor (the reason this happens is discussed in detail below).
One way that was tried to address this saturation problem was to install an optical attenuator (e.g., variable optical attenuator (VOA)) within the launch system to reduce the intensity of the emitted light to a level which is below the saturation limit of the CCD array (e.g., pixels) within the spectrometer. However, the optical interrogation system has a signal-to-noise ratio (SNR) per unit of integration time which happens to be limited by the intensity of the light received at the CCD array in the spectrometer. Thus, the spectrometer's ability to locate the optical resonance is quantifiably related to the amount of power that the CCD array (pixels) is able to handle without saturating. As a result, if the spectrometer could be enhanced to handle a higher optical power level then it would be possible to detect small shifts in the optical response and hence detect small biological events on top of the RWG sensor. This need is satisfied by the present invention.